Yes, another planet, an exact mirror image of our Earth, appears in our Universe.
On the same night that it appears, a car accident takes the life of a composer's wife. Instead of focusing on what everyone does about the existence of this duplicate Earth, the movie covers in depth the guilt felt by the woman driving the other car; how she spends the next few years in jail for causing the accident, then the year after getting out of jail cleaning the composer's house and getting "involved" with him, all without him knowing who she really is.
Full marks for a story that manages to cover a huge science fiction topic without a shred of science.
An intensely miserable film, which left me feeling that the other Earth was just an arty farty light against which to hold a sad tale about guilt and grief.
An ending that could spark hours of interesting debate doesn't really save this from being too slow, and a bit dull.